Skip to main content

Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

See other formats


COLUMBIA GLACIER                                        275
ridden. Measurements made from the glacier edge to a blazed tree at the base of a neighboring hill showed an advance here of 20 feet from July 9th to September 5th, the rate being slower than in July, probably because the glacier was advancing up a steep slope during the latter period. On September 5th the ice edge was only 13 feet from the tree, which is blazed on the side away from the glacier.
The remainder of this portion of the ice edge was bordered in 1910 by a strip of mud, covering the terminus of the glacier. There was a series of mud flows of varying liquidity depending upon the amount of water from the melting ice, some of them flowing out into the borders of the forest, overwhehning the shrubs and rising up around the trunks of the trees. Near the eastern edge of the timber belt the mud flows were crowding in against a high bank, along which they rose appreciably higher in September than in July, 1910.
In the cove between the eastern end of Heather Island and the small island to the .north of it the glacier ended in a low, dirty, sloping front instead of in a clean, precipitous cliff. The actual terminus was upon inorainic shoals and tidal mud flats so that the water came up over the end of the glacier at high tide; but at low tide the cove had no water except a narrow shallow stream flowing down the middle. Near the glacier were many mud flows, and the whole cove, or lagoon, was floored by fine glacial mud across which it was possible to walk at low tide. Scattered through it were a few bowlders dropped by icebergs which floated in the cove at high tide, and upon its surface there were iceberg pits and long, sinuous trails left by the dragging of icebergs during the rising and falling tide. None of these icebergs were discharged from this part of the glacier but floated in from the larger bay to the east. Numerous small streams emerging from this part of the glacier were helping to fill the cove with glacial mud.
This cove was narrowed considerably by the advance of the glacier from August, 1909, to July, 1910, and from the latter date to September, 1910, as the three photographs of PI. CXI clearly show.
That this part of the ice front extended farther out a number of years ago is indicated by a morainic island extending at right angles to the present glacier terminus and not now covered at high tide. It has no trees or other vegetation, except annual plants, and is the only land close to the ice front that has neither trees nor thick heather; but the annual plants that grow upon it, show that the tide does not rise over it now. Gilbert says 1 that in 1899 "a bank also extended eastward from the island against which the ice front rested, constituting at low water a stony cape half a mile long near the foot of the ice cliff." His description and photograph do not harmonize with our observations in 1909, for the bank was surely an island then. It is possible that this part of the glacier has advanced to the island since 1899, for no other cause for raising it above high tide is possible, excepting uplift. Recent advance to the morainic island is indicated by the presence of a sinuous ridge of gravelly material on the side next the ice front. This deposit may possibly represent either an esker or a. push moraine. The latter seems the more probable, for in July, 1910, the advancing ice front was building a low push moraine with a series of minor lobes which had narrow crests and very angular turns, similar to those in the higher, sinuous deposit of older date.
In front of the ice there was a broad, low arch of stiff mud with marine shells, pushed up between August, 1909, and June, 1910, across which an antecedent stream had cut a
0p. cit., p. 75.